1. Field of the Invention
The present invention relates to apparatus for automatically retrieving desired information contained in a film by the detection of retrieval marks provided on the film.
2. Description of the Prior Art
The above-mentioned type of retrieving apparatus is known in the art and is often used in a microfilm reader. Generally, the film for use in such retrieving apparatus has marks provided along one or both sides of the film in the relation of one mark to one frame. In retrieving the frame having the desired information to be retrieved, the marks are detected one by one by a mark detector and the detected marks are serially counted by a counter.
The operator makes an input of the number of the desired information by the keyboard of the apparatus to start the retrieving operation. The film is then moved and the marks on the film are illuminated. The mark detector having one or more photoelectric transducer elements detects the light signal from the mark and produces a detection signal which is applied to the counter. The content of the counter and the input information number are continuously compared with each other by a comparator. When the content of the counter becomes equal to the number of the desired information, the comparator issues a stop signal which is applied to a drive control circuit. In response to the stop signal, the control circuit stops the film driving system. Thus, the desired information is located at a determined position where the information is projected on a screen.
In practical use of the above-mentioned type of information retrieving apparatus, however, there is a difficult problem relating to the retrieval marks provided on the film. Until now, the marking mode (size, form and position) or retrieval marks on the film has not been standarized. Therefore, the films for use in the above retrieving apparatus available on the market at present are not the same in the marking mode. There are used many different marking modes. This means that only one kind of film can be used in one retrieving apparatus. If another kind of film is used in the retrieving apparatus, it will cause some troubles. For example, the film may be stopped at a position deviated from the determined stop position or the apparatus will fail to retrieve the desired information.
The problem can not be solved in a simple manner. It will be required that a film reader be provided with many retrieving apparatus corresponding to many different kinds of films having different marks in respect of the shape and position of the mark. Of course, this solution involves the problem of extremely high cost. Otherwise, it will be required to exchange from one mark detector into another mark detector according to the kind of the film then loaded on the apparatus. However, this solution often leads the operator to a mistake in selecting the mark detector. If the operator once selected any wrong mark detector to the film in which the desired information is to be retrieved, there would occur the same trouble as above. For example, again the film may be stopped at a wrong position for the desired information or the retrieving apparatus may fail to retrieve the desired information.
On the other hand, at present there are two different types of films adapted for the information retrieving apparatus. One is the type in which one and the same kind of marks are provided for all pieces of information contained in a film. The marks to be detected are all the same in size and form. The other type is of such film in which a great number of pieces of information recorded thereon are classified into a plural number of groups according to the item of information, and different kinds of marks having different sizes are provided for different groups in the same film. In case of the second type of film, any desired information in the film can be retrieved when the operator makes an input of the retrieval number of the item allotted to the information. For instance, a relatively small size mark is provided for every information classified in a subitem and a relatively large size mark is provided for every information classified in the item. When the operator makes an input of the retrieval number of a subitem and the retrieval number of the item of the desired information, the apparatus retrieves the desired information classified in the subitem and in the item. When the operator makes an input of the retrieval number of the item only, the apparatus retrieves the desired information classified in that item.
If the operator erroneously makes an input of a retrieval number of the second type of film into the apparatus which has now a film of the first type therein, the apparatus can not correctly work for retrieving the desired information. In such case, the apparatus will retrieve wrong information or continue to drive the film up to the end because of the absence of the information corresponding to the input retrieval number. The operator can not become aware of his mistake before the wrong information has been retrieved by the apparatus or the film has been fed vainly up to its end. Therefore, it takes a long time before the operator has become aware of such mistake. This reduces the efficiency of the retrieving work to a great extent. Those operators who are not skilled in the retrieving work often make such mistake.